1. Field of the Invention
The present invention relates to an optical fiber wiring board for optically connecting optical elements, optical circuits or optical devices to each other.
2. Description of the Related Art
Improvement of transmission rate has been intended in the inside of communication apparatus and computers in recent years. Examination of optical interconnection substituted for electric wiring heretofore used has been advanced for high-rate transmission. At present, a proposal has been made on an optical fiber wiring board in which a large number of optical fibers are arranged as wiring in a backboard or in a plug-in unit so as to be integrated into the form of a board. Such an optical fiber wiring board generally is formed as follows: A large number of optical fibers are arranged as wiring on a sheet-like substrate provided with an adhesive layer. Then, at least one optical fiber is led out at a predetermined position from an edge portion of the substrate. When a plurality of optical fibers are led out at the predetermined position, they are led out in a condition that they are horizontally arranged in a row. Finally, connectors are attached to the ends of the optical fibers thus led out.
As a structure of leading out the optical fibers, a following configuration has been disclosed in Japanese Patent No. 2574611. That is, tab portions in form of protrusion portions are provided on optical fiber leading-out portions of the substrate so that optical fibers are extended out along the tab portions. In this configuration, the optical fiber leading-out portions can be mechanically reinforced with the tab portions. Moreover, the optical fibers extended out from the substrate can be pulled around when the tab portions are curved in a direction vertical to the plane of the substrate or twisted. Therefore, there is an advantage that degree of freedom in points of connection of connectors is increased.
In the configuration, the degree of freedom for curving the tab portions in a direction vertical to the plane of the substrate is obtainable. However, the tab portions cannot be curved in a left-right direction with respect to a direction in which the tab portions are protruded out from the substrate because the tab portions protruded out from the substrate are formed integrally with the substrate. There is a disadvantage that the degree of freedom is limited when optical fibers are pulled around from the optical fiber leading-out portion in a direction horizontal to the plane of the substrate and connected by connectors connected there to. It may be therefore considered that extension portions are constituted by optical fibers which are simply led out from the substrate without provision of any tab portion. If such extension portions are pulled around for connection of connectors, excessive bending is, however, applied on the optical fibers to thereby bring about a problem in increase of loss or damage of the optical fibers.
Therefore, an object of the invention is to provide an optical fiber wiring board having an optical fiber leading-out structure in which a bundle of optical fibers led out from a substrate can be pulled around freely in a direction horizontal to the plane of the substrate as well as in a direction vertical to the plane of the substrate, and in which the optical fibers extended out from the substrate can be mechanically reinforced sufficiently.
In order to accomplish the object above, the following means are adopted. According to the invention, there is provided an optical fiber wiring board comprising: a substrate; a plurality of optical fibers arranged as wiring on the substrate; a extension portion including a base portion having a predetermined length from an edge portion of the substrate, and a forwarding end portion connected to a side of the base portion opposing the substrate wherein the extension portion also includes at least one optical fiber; a protective tube protecting the optical fiber in the extension portion; and a lock portion provided in the edge portion of the substrate for locking one end portion of the protective tube relative to the substrate.
In the optical fiber wiring board, one optical fiber may be led out in the extension portion or a plurality of optical fibers may be led out in the extension portion. In the case of a plurality of optical fibers contained in the extension portion, the optical fibers are preferably led out horizontally closely to one another in a row so that the adjacent optical fibers are integrated with each other over the whole or partial length of the optical fibers in the extension portion.
In the configuration, a bundle of optical fibers can be curved freely in the extension portion because a holding body such as the tab portion integrated with the substrate is not attached to the optical fibers led out. Accordingly, the optical fibers led out from the substrate can be pulled around freely in directions horizontal and oblique to the plane of the substrate as well as in a direction vertical to the plane of the substrate. In addition, because the optical fibers in the extension portion are covered with the protective tube, the optical fibers can be protected from bending stress or damage due to pulling around of the optical fibers for connection of connectors so that the mechanical strength of the extension portion is reinforced.
When a plurality of optical fibers are led out in one extension portion, the optical fibers may be led out horizontally closely to one another in a row so that the adjacent optical fibers are integrated with one another over the whole or partial length of the optical fibers in the extension portion. In this case, a bundle of optical fibers led out is wholly or partly fixed integrally, for example, to form a tape-like shape. Therefore, the bundle of the optical fibers is not separated into pieces. Moreover, the state of arrangement of the optical fibers in the portion in which the optical fibers are led out from the substrate is not disordered. Further, the portion fixed integrally may be limited to a forward end portion of the optical fibers led out so that a base portion of the optical fibers can be made free. In this case, the degree of freedom for curving can be preferably kept in the base portion.
In the above-mentioned optical fiber wiring board, it is preferable that the lock portion includes notch portions formed at portions in the substrate, between which the optical fiber is extended out from the edge portion of the substrate, wherein the one end portion of the protective tube is fitted and locked to the notch portions. In such a lock structure, there is required only a simple operation that one end of each of the protective tubes put on the optical fibers in the extension portions is attached to corresponding ones of notch portions formed in the substrate before the connectors are attached. Hence, there is an advantage that workability is excellent.
A heat-shrinkable tube is preferably used as the protective tube. In this case, the heat-shrinkable tube may be heat-shrunk after one end portion of the heat-shrinkable tube is fitted into the lock portion of the substrate. After heat shrinking, the tube is made thin in the portion locked to the substrate. Hence, a level difference between the tube and the substrate is reduced. Moreover, the adhesive property between the inside of the tube and the substrate/optical fiber is made good. Hence, tolerance to dropout is preferably improved.
Further, the above-mentioned optical fiber wiring board, preferably, further comprising: a loose tube protecting the optical fiber in the extension portion, wherein the loose tube is covered with the protective tube. In the optical fiber wiring board, the protective tube may cover integrally a plurality of loose tubes each protecting the optical fiber in each of the extension portions.